Texas is a region of complex earth structures as indicated by the outcropping rocks ofdifferent geologic ages. Map shows the areas in which the principal outcroppings occur. It isa reduction of the Geologic Map of Texas, by E. H. Sellards, W. S. Adkins and F. B. Plummerof the Bureau of Economic Geology, University of Texas.

syncline (See right-hand part of chart. p.95) and its subordinate East Texas Embay-ment and Rio Grande embayment; third, themountains of the Rocky Mountain system,framing the west edge of the Permian Basin(west edge of the chart on p. 95) and ofthe Coastal plains of northern Mexico; fourth.,the Amarillo-Wichita-Muenster Mountains;and fifth, the broad complicated zone whichlies between the Permian Basin on the north-west and the Gulf Coastal Plain on the south-east. This zone comprises the Marathon andassociated mountains, the Bend Arch, theCentral Mineral Region, and in part theOuachita (Pennsylvanian) geosyncline and thefolded roots of the Llanorian Mountains in it.(See center section of chart, p. 95.)Reservoirs of Wealth.The geologic activity of the ages has hadan important bearing on the economic life ofTexas of today because of the soils producedby the weathering of the stone and becauseof the deposits of minerals that today makeTexas the leading state in mineral produc-tion. The abundant fuel resources of Texas-oil, gas, coal and lignite- came from the ma-rine life and the dense plant growth thatflourished alternately as ancient Texas exist-ed beneath the surface of the sea and as dryland. The folding, bending and faulting ofstrata caused the oil to collect in pools and

stand until man's inventive genius sent drill-ing tools down to release it for use. The saltdomes of the coast country-great pillars thatrise from unknown depths almost to the sur-face-have formed oil pools and also broughtnear the surface deposits of sulphur thatmake Texas one of the greatest sulphur-pro-ducing areas of the world.A varied and highly valuable quantity ofigneous and sedimentary stone has been be-queathed by the long succession of geologicages that have seen molten matter flowthrough fissures in the earth's crust, andstratum after stratum of sedimentary matterdeposited as the land emerged from the sea,sank and rose again, and mountains werethrust upward to be eroded to level plains.Sand and porous stone strata sealed by claysand hard stone are the reservoirs of Texas'great underground water supply.Geology, once a highly academic and theo-retical science, is today one of great practicalsignificance. At the same time, geology hasprogressed from a status of guesswork andassumption based on surface indications toone of relatively definite information, duelargely to the drilling of deep wells for pe-troleum. Because of the widespread drillingin Texas, there is much concrete informationabout the intricate layers and folds of earthstructure that lie deep beneath the surface.